It's going to be a warm dry lead up to Christmas with not too much wind, aided by returning La Nina conditions in the tropical Pacific, says the National Institute of Water and Atmospheric research in its October-December outlook.

Average to above-average temperatures are expected with normal or below-normal rainfall forecast as the La Nina conditions return.

The tropical Pacific returned to neutral conditions following the La Nina event over July 2010 to April 2011.

Over the last 4-6 weeks there's mounting evidence of a transition back to La Nina conditions.

The Southern Oscillation Index has become more positive. Sea surface temperature anomalies have become increasingly negative in the east-central equatorial Pacific, and the easterly trade winds have intensified near the date line.

There's been a major shift in the consensus from global climate models which predict El Nino-Southern Oscillation conditions.

The majority of these models are now forecasting further development of La Nina patterns over spring and a continuation through the summer of 2011/12.

The intensity is not known at this early stage.

Farmers are warned that soil moisture levels and river flows are likely to be below normal in all regions of the country, except for the west and south of the South Island where normal or below normal soil moisture levels are likely.

Soils are already drier than normal for this time of year in north Canterbury, MacKenzie country and central Otago, as well as parts of the North Island.

Temperatures for October-December are likely to be average or above average in the North Island and northern South Island, and near average in the rest of the South Island.

La Nina conditions redeveloping in the tropical Pacific are expected to build through spring and continue over the summer season, according to the NIWA National Climate Centre.

Mean sea level pressures during the October-December period as a whole are likely to be above normal across New Zealand, with weaker westerlies over the country.

Air temperatures for October-December are likely to be average or above average in the North Island and in Nelson-Marlborough.

For the remainder of the South Island, temperatures are likely to be near average.

Sea surface temperatures near New Zealand are expected to be close to normal or slightly above normal through the period.

In Northland, Auckland, Waikato, Bay of Plenty, temperatures are likely to be average or above average for the time of year. October to December rainfall totals are equally likely to be in the normal or below normal range.

Soil moisture levels and river flows are likely to be below normal.